Interferon is an important antiviral and antitumor protein produced by the body. Because of its species specificity, clinical use of interferon requires human interferon. The limited amount of interferon that can be produced from tissue culture cells or from fresh white blood cells, is not sufficient for large-scale clinical use. Introduction of the genetic information for human interferon into a bacterial microorganism could possibly, if it were available, allow the mass-production of a polypeptide having interferon activity. It is known that such techniques have been developed for human growth hormone and insulin.
The two types of interferon, i.e. leucocytes (IFN-.alpha.) and fibroblast types (IFN-.beta.) appear to be coded by different messenger RNAs (Cavallieri et al., 1977, Proc.Natl.Acad.Sci.USA 74, 4415-19). Isolation of these mRNAs in pure form has not been achieved as yet. This appears to be all the more difficult as the host cell is liable of synthesizing the interferon mRNA only as a result of exposure of the latter to suitable exogenous factors, for instance, viral infection or particular experimental polynucleotides such as poly (rI:rC), and only in minute amounts. Accordingly, if it had already been suggested to use a mRNA extract of host cells which had preliminarily been induced to produce interferon and to cause it to be translated in vitro in a cell-free system comprising all ingredients, particularly the natural aminoacids, whereby a protein preparation having interferon activity had been obtained, the interferon mRNA was indeed but a very minor proportion of the mRNAs being translated and accordingly the final protein preparation having interferon activity was more than highly contaminated with other proteins.
Therefore, the use of the mRNA preparations of the prior art as a starting material for direct transforming into double stranded DNA liable of being cloned after its insertion in a suitable vector, would involve screening difficulties which would be insuperable in practice.